While HTTP/2 multiplexed requests over a single TCP socket, transport-level packet losses still stalled concurrent streams due to TCP ordered-delivery semantics.

HTTP/3 adopts QUIC running over UDP as its transport mechanism.

1. Stream-Level Independence

QUIC tracks individual streams at the transport layer, ensuring that a dropped packet delays only the affected stream without impeding parallel transactions.

2. Unified Handshake and Connection Migration

By embedding TLS 1.3 within connection establishment, QUIC reduces setup round trips and maintains state across IP changes via persistent Connection IDs.